This invention relates to stents, urology, and treatments for benign prostate hypertrophy or prostate cancer, as well as methods for correction of vessel occlusions.
Prostate enlargement, also known as benign prostate hyperplasia or benign prostate hypertrophy, is a common affliction among older men. The condition involves swelling of the prostate. The prostate surrounds the urethra, or urinary tract, and swelling of the prostate prevents passage of urine from the bladder. Benign prostate hyperplasia is uncomfortable because it makes urination difficult or impossible. The condition is also dangerous because it can lead to infection of the bladder and kidneys, and severe cases may lead to death. Prostate cancer is also a common affliction among older men, and may lead to many of the same symptoms as benign prostate enlargement. Prostate cancer is more dangerous in that it may spread to other organs and is often fatal. Early treatment can reduce the risks of death due to prostate cancer.
Both prostate enlargement and prostate cancer can be treated with heat treatments such as hyperthermia or thermotherapy. As described in our co-pending U.S. application Ser. No. 08/629,650 filed Apr. 9, 1996, a stent serves the dual purpose of acting as a heat source for the thermotherapy procedures, as well as acting to hold the urethra open after therapy to prevent blockage due to swelling and prostate tissue sloughing. A stent may be implanted as an interim solution to hold open the urethra while the patient awaits more aggressive surgery or treatment. A stent may be implanted after hypothermia or cryosurgery to keep the urethra open while enlargement subsides. Finally, a stent may be implanted as a primary treatment.
When the stent is implanted for any of these reasons, it is usually better to leave the bladder neck sphincter and the external sphincter un-blocked by the stent. These sphincters control the flow of urine through the urethra, and if the stent is placed within these sphincters they will not be able to close. This would leave the patient incontinent. To ensure the proper positioning of the stent, the devices below provide several benefits including controlled release of the stent, tentative initial opening of the stent, and visualization of the bladder and prostatic urethra during placement.
McNamara, et al., Nitinol Stent For Hollow Body Conduits, U.S. Pat. No. 5,147,370 (Sep. 15, 1992) describes a catheter delivery system which uses a single pullwire to retain and release a stent wrapped on the distal end of a catheter. The stent must be provided with xe2x80x9cretaining meansxe2x80x9d in the form of pigtails or hooks on the stent ends capable of engaging a pullwire. The catheter must have two holes communicating into a lumen within the catheter, and the stent ends must enter the lumen through the holes. The pullwire is in the lumen, and engages the stent ends which enter the lumen. After release into the lumen, the retaining means are left to hang in the body lumen. This could lead to thrombus formation in blood vessels and undesirable deposition in urethral stents unless addition precautions are taken to avoid the complications. While materials may be developed in which the stent retaining pigtail structures are not set into the form of the stent, common stent alloys such elgiloy, nitinol and stainless steel will take a set in the form of pigtails if deformed as suggested by McNamara.
Hillstead, Apparatus And Method For Placement Of A Stent Within A Subject Vessel, U.S. Pat. No. 4,913,141 (Apr. 3, 1990) discloses a stent delivery device which uses a pullwire running through the central lumen of the catheter and exiting the catheter to run over the stent ends. The stent is deployed by pulling the pullwire proximally, requiring the pullwire to course over intimal and endothelial surfaces of the body lumen to be treated. This could lead to damage of lumenal surfaces and attendant healing responses which are undesirable. Neither McNamara nor Hillstead provide a mechanism which permits retention and release of the stent with a mechanism which remains in the annular space of the stent, and do not present radially extending features such as the radially outwardly protruding pullwires or radially inwardly protruding pigtails.
The stent delivery systems described below permit placement of stents in the urethra and other body vessels. The devices are intended to deploy a shape memory stent or other resilient stent into the prostatic urethra under direct vision. The surgeons who use the stent delivery systems can easily place the stent within the prostatic urethra and make sure that the stent does not block the bladder neck sphincter. The stent is retained on the catheter with a retaining wire or rod which engages the stent ends as the stent ends protrude into recesses in the catheter walls. The catheter is comprised of two coaxial tubes, one inside the other, and the distal end of the stent is secured to the inner tube while the proximal end of the stent is secured to the outer tube. When both ends of the stent are secured to their respective tubes, the tubes may be rotated relative to each other to open the stent or tighten the stent. The stent may be released from the catheter by pulling the pull wires proximally out of engagement with the stent ends. The pull wire which retains the distal end of the stent is release first, and the location of the distal end of the stent is observed. Once the distal end of the stent is located properly, the proximal end of the stent is released from the catheter by pulling the pull wire which retains the proximal end of the stent out of engagement with the proximal end of the stent.